Photoresist polymers having nitro groups (xe2x80x94NO2), and photoresist compositions containing the same are disclosed. More specifically, photoresist polymers used in a photoresist for VUV (vacuum ultraviolet processes), and photoresist compositions containing the same are disclosed.
Photoresist compositions of a chemical amplification type, which are prepared by incorporating photoresist polymers of a structure that sensitively reacts with acid, photoacid generators and organic solvents, are widely used for photolithography manufacturing semiconductors.
The reaction mechanism of the chemical amplification type photoresist is examined by referring to a positive photoresist. In the light-exposed area, the photoacid generator, as lighted by the ultraviolet light source generates acid, which releases the acid labile protecting group of the polymer and dissolved into the developing solution, while the non-exposed area, not radiated by ultraviolet light, retains its original structure even after being treated with developing solution. Thus, the image of the mask is revealed as positive pattern in the substrate.
In the photolithography process, the resolution depends on the wavelength of light source. As the wavelength of light source decreases, a smaller pattern can be formed. Thus, a photoresist suitable for such a light source is required.
In general, a photoresist polymer to be used as a photoresist for VUV processes should have low light absorbance at 157 nm wavelength, good etching resistance and adhesive property, and should be able to be developed by conventional developing solution such as 2.38 wt % or 2.6 wt % aqueous tetramethylammonium hydroxide (hereinafter, abbreviated to as xe2x80x9cTMAHxe2x80x9d) solution.
Photoresist polymers contained in conventional photoresists (i-line (356 nm), KrF (248 nm) and ArF (193 nm)), for example, polyhydroxystyrene and novolac resin have satisfied every physical properties required for a photoresist. However, the photoresists comprising such photoresist polymers shows intense absorbance in the range of 157 nm wavelength, so they cannot be used as a photoresist for VUV.
Studies on ethylene type polymers, styrene type polymers and acrylate type polymers containing fluorine have been actively performed. However, these ethylene type polymers, styrene type polymers and acrylate type polymers containing fluorine have disadvantages of weak etching resistance, and low solubility in aqueous TMAH solution, difficulties in its development, and low adhesive property to silicon wafer. In addition, these polymers impose various problems such as difficulties of mass production and high price, thereby they are not suitable for industrial use as of yet. Further, a photoresist which comprises silicon-containing polymer cannot be suitably used as a photoresist since it induces the problem of lens contamination due to outgassing.
In order to solve the problems of conventional arts as described above, nitrated polyhydroxystyrene and novolac resin are disclosed with a lower absorbance at 157 nm wavelength, and the hydrogen of the hydroxy group of the nitrated polyhydroxystyrene or nitrated novolac resin is substituted with a proper ratio of acid labile protecting group to control the solubility in developing solution, thereby providing a novel photoresist polymer and a photoresist composition containing the same, that can be used as a photoresist for VUV.
In addition, a process for forming a photoresist pattern by using said photoresist composition, and a semiconductor element obtained according to said process are also disclosed.
Thus, a novel photoresist polymer comprising a polymerization repeating unit containing nitro groups, a process for preparing the same, a photoresist composition comprising said polymer, a process for forming a photoresist pattern by the use of said composition, and a semiconductor element prepared according to said process for pattern formation are also disclosed.